Using brain scans, scientists ...have uncovered physiological evidence for "chemo brain", a common and often debilitating side effect of cancer chemotherapy treatment that patients often describe as a "mental fog". With the help of positron emission tomography combined with computed tomography (PET/CT), the [research] team found that following chemotherapy, areas of the brain involved with planning and decision-making use less energy.....[W]hile the complaint may be common, scientists have struggled to pinpoint its causes. Some have had success with MRI...scans, and identified some small changes in brain volume after chemotherapy, but nothing definite. [Researchers have now] decided to try a different approach: instead of examining what the brain looks like after chemo, they examined changes to its metabolism, or how it uses energy, using a PET/CT combination....The analysis reveals a statistically significant link between reductions in regional brain metabolism and symptoms of chemo brain. [The lead researcher] says their findings show "there are specific areas of the brain that use less energy following chemotherapy". These brain areas are the ones known to be responsible for planning and prioritizing," she adds.The researchers hope their PET/CT approach will be used to diagnose chemo brain so patients receive help sooner.

As has been emphasized here on previous occasions, it always helps to have a diagnostic method to pinpoint a particular syndrome such as PCCI. A firm diagnosis helps to reassure a patient that they are suffering from a known malady. In addition, such a diagnostic method helps to assess various treatment modalities and drugs that are being tested to improve the condition. Proper treatment for PCCI is still unclear. Here's a quote from the Wikipedia article about the topic (see: Post-chemotherapy cognitive impairment) :

Hypothesized treatment options include the use of antioxidants, cognitive behavior therapy, erythropoietin and stimulant drugs such as methylphenidate, though as the mechanism of PCCI is not well understood the potential treatment options are equally theoretical. Modafinil, approved for narcolepsy, has been used off-label in trials with people with symptoms of chemobrain. Modafinil is a wakefulness-promoting agent that can improve alertness and concentration and appears to be effective at least among women with breast cancer. While taking estrogen will frequently reverse the symptoms when they appear in women with breast cancer, this carries health risks, including possibly promoting the proliferation of breast cancer cells.